This invention relates to a display control technique which is particularly effective when applied to a multi-window control system. More particularly, it relates to a technique which is effective when utilized for a display control apparatus, such as a graphic controller, for example.
In conventional graphic display systems, both software window systems and a hardware window systems have been proposed as a multi-window control system for displaying a plurality of windows on a display surface.
Among them, the hardware window system is accomplished by furnishing a display controller LSI with a multi-window control function. In the software window system, on the other hand, software executes a function called "bit block transfer" which transfers data of a rectangular region inside a frame buffer for the purpose of multi-window display. (As to multi-window control, refer to "Nikkei Electronics", published by Nikkei McGraw Hill Co., July 14, 1986, No. 399, pp. 115-132).
In the conventional multi-window control systems, the hardware system has a higher display speed but its display freedom is lower because the priority sequence of windows is fixed. On the other hand, the software system has high freedom of display surface, such as a greater number of windows, but involves the problem that the display speed is extremely low for the following reason. In the software system, data that constitute a base picture and a window picture are stored in predetermined areas of a bit map memory, respectively, and then the display surface area must be rewritten through data block transfer by transferring the data constituting the window picture to the base surface area and superposing them together.